1. Field of the Invention
The present invention is concerned with a blue-light emitting material and with an organic light-emitting device containing the same.
2. Related Technology
A typical organic light-emitting device (OLED) comprises a substrate, on which is supported an anode, a cathode and a light-emitting layer situated in between the anode and cathode and comprising at least one polymeric electroluminescent material. In operation, holes are injected into the device through the anode and electrons are injected into the device through the cathode. The holes and electrons combine in the light-emitting layer to form an exciton which then undergoes radioactive decay to emit light.
Other layers may be present in the OLED, for example a layer of hole injection material, such as poly(ethylene dioxythiophene)/polystyrene sulphonate (PEDOT/PSS), may be provided between the anode and the light-emitting layer to assist injection of holes from the anode to the light-emitting layer. Further, a hole transport layer may be provided between the anode and the light-emitting layer to assist transport of holes to the light-emitting layer.
Luminescent conjugated polymers are an important class of materials that will be used in organic light emitting devices for the next generation of information technology based consumer products. The principle interest in the use of polymers, as opposed to inorganic semiconducting and organic dye materials, lies in the scope for low-cost device manufacturing, using solution-processing of film-forming materials. Since the last decade much effort has been devoted to the improvement of the emission efficiency of organic light emitting diodes (OLEDs) either by developing highly efficient materials or efficient device structures.
A further advantage of conjugated polymers is that they may be readily formed by Suzuki or Yamamoto polymerisation. This enables a high degree of control over the regioregulatory of the resultant polymer.
Blue light-emitting polymers have been disclosed. “Synthesis of a segmented conjugated polymer chain giving a blue-shifted electroluminescence and improved efficiency” by P. L. Burn, A. B. Holmes, A. Kraft, D. D. C. Bradley, A. R. Brown and R. H. Friend, J. Chem. Soc., Chem. Commun., 1992, 32 described the preparation of a light-emitting polymer that had conjugated and non-conjugated sequences in the main chain and exhibited blue-green electroluminescence with an emission maximum at 508 nm. Blue light-emission was observed in two conjugated polymers. Poly(p-phenylene) sandwiched between indium-tin oxide and aluminium contacts has been published by G. Grem, G. Leditzky, B. Ullrich and G. Leising in Adv. Mater. 1992, 4, 36. Similarly, Y. Ohmori, M. Uchida, K. Muro and K. Yoshino reported on “Blue electroluminescent diodes utilizing poly(alkylfluorene)” in Jpn. J. Appl. Phys., 1991, 30, L1941.
Applied Physics Letters, Vol. 75, No. 26, 27 December 1999, 4055-4057 “Reduction of molecular aggregation and its application to the high-performance blue perylene-doped organic electroluminescent device” discloses electroluminescent devices made using perylene as adopant in bis(2-methyl-8-quinolinolato)(para-phenylphenolato) aluminium (III).
WO 00/55927 discloses an organic polymer having a plurality of regions along the length of the polymer backbone and comprising two or more of the following:                (i) a first region for transporting negative charge carriers and having a first bandgap defined by a first LUMO level and a first HOMO level; and        (ii) a second region for transporting positive charge carriers and having a second bandgap defined by a second LUMO level and a second HOMO level; and        (iii) a third region for accepting and combining positive and negative charge carriers to generate light and having a third bandgap defined by a third LUMO level and a third HOMO level,        wherein each region comprises one or more monomers and the quantity and arrangement of the monomers in the organic polymer is elected so that the first, second and third bandgaps are distinct from one another in the polymer. There is no mention of perylenes.        
J. Am. Chem. Soc., 2003, 125, 437-443 “Attaching Perylene Dyes to Polyfluorene: Three Simple, Efficient Methods for Facile Color Tuning of Light-Emitting Polymers” discloses attachment of perylene dyes to polyfluorene chains either as (i) comonomers in the main chain, (ii) as endcapping groups at the chain termini, or (iii) as pendant side groups.
Polymer (Korea), 2004, 28(5), 367-373 “Electroluminescence characteristics of blue light emitting copolymer containing perylene and triazine moieties in the side chain” discloses blue light emitting copolymers containing perylene and triazine moieties as light emitting an electron transporting units in the polymer side chain.
Chem. Commun., 2005, 2172-2174 “Selective Ir-catalysed borylation of polycyclic aromatic hydrocarbons: structures of naphthalene-2,6-bis(boronate), pyrene-2,7-bis(boronate) and perylene-2,5,8,11-tetra(boronate) esters” discloses the production of pyrene-bis(boronate) and perylene-tetra(boronate) esters to produce conjugated systems and optical materials.